1. Field
Apparatuses and methods consistent with exemplary embodiments relate to time synchronization, and more particularly, to synchronizing a time of a network camera with a time of a network video recorder (NVR) by analyzing timestamps of image and audio frames received from the network camera and, when an expected timestamp is not received, correcting this problem.
2. Description of the Related Art
Image monitoring systems using surveillance cameras such as closed-circuit television (CCTV) and network systems that transmit image and audio data using networks are being rapidly disseminated. An image monitoring system or a network system registers a recording schedule to store image data obtained by a camera. When a user designates a hard disk to store the image data, the image data is stored in files in order of time on the designated hard disk. Then, when the designated hard disk is full, oldest data is removed from the hard disk, and new data is stored instead.
Here, an image system should be operated by synchronizing a timestamp of an NVR with timestamps contained in image and audio frames sent from multiple network cameras having different formats or times. To this end, the format diversity of time information input from a network camera, the difference in reference time, and errors of the time information should be corrected.
Until now, the difference between timestamps of image and audio frames received from a network camera and a timestamp of an NVR has been corrected simply by sensing a network jitter. In this case, however, an image system for image recording and event monitoring may have time errors due to temporary timestamp errors of frames generated by the camera or the timestamp difference between the camera and the NVR. These time errors may hinder the NVR from recording images or monitoring events at the right time.